Discontinuous box foam processes are used to produce water-blown open-celled polyurethane foams used in many applications, such as, for example, automotive hoodliners, headliners and sun shades. In this process, a water-blown polyurethane foam-forming composition is deposited, often by pouring, into a large box and allowed to rise and form an open-celled polyurethane foam, often referred to as a “bun”, in the box. The exothermic polyurethane foam-forming reaction generates heat. After the foam sets, a degas process takes place by sudden evaporation of a mixture of steam and CO2, leaving a number of small craters on the surface of the slab. This blow-out process is the outward sign that the foam cells have opened. After an additional 30 minutes or so, the bun is then typically removed from the box and allowed to cool at ambient conditions for roughly 24 to 48 hours. Once the foam bun has cooled, it is sliced to sheets of the desired thickness for the end product, such as an automotive hoodliner, headliner, and/or sun shades. Prior to such slicing, however, the sides and top and bottom of the bun are typically trimmed to square off the bun. This trimmed foam is generally waste.
One area of difficulty in such discontinuous box foam processes to produce water-blown open-celled polyurethane foams is the degree of waste generated at the bottom of the bun. Water reacts with the polyisocyanate in the composition during foam formation, which produces carbon dioxide. This carbon dioxide can generally escape from the upper portions of the open-celled polyurethane foam bun, but more often becomes trapped in the bottom portion which creates large voids in the bottom portion of the bun following the degas process, resulting in a foam having a poor appearance and significantly lower density at the bottom of the bun relative to other portions of the bun. The portion of the bottom of the bun containing these large voids is waste.
Attempts have been made to minimize the waste produced from the bottom of the bun in such processes. For example, chemical modifications of the polyurethane foam-forming composition, such as manipulation of surfactant and/or catalyst in the composition, have been attempted to increase cell tightness. A problem with these compositional approaches, however, is that increasing cell tightness throughout the entire bun can have a detrimental effect on physical properties of the resulting foam and also can detrimentally effect properties, such as acoustic properties, of the article, such as automotive hoodliner, headliner and/or sun shade, produced from the foam.
As a result, it would be desirable to provide an improved discontinuous box polyurethane foam process that reduces the amount of waste at the bottom portion of the polyurethane bun without making chemical modifications of the polyurethane foam-forming that could have a detrimental impact on the physical properties of the resulting open-celled polyurethane foam bun or articles produced from such a foam.